Electric resistance device



Nov. 17, 1931. H. FENDER ELECTRIC RESISTANCE DEVICE Original Filed May1925 an, Wm 9 62. qw ATTORNEY Patented Nov. 17, 1931 UNITED STATESPATENT OFFICE HAROLD FENDER, OF IEBION, PENNSYLVANIA, ASSIGNOB- '10TN'TERNATIONAL IBE- SISTANCE COMPANY, OF PHILADELPHIA, PENNSYLVANIA, ACORPORATION OF DELAWARE ELECTRIC RESISTANCE DEV ICE OriglnaI applicationfiled Kay 28, 1926, Serial No. 88,327. latent No. 1,771,055, dated July20, 1980.

vided and this application flledlugust 16, 1929. Serial No. 386,384.

This invention relates to electrical resistance devices or media.

One of the objects of this invention is to provide a medium ofhighelectrical resistance which is practical, uniform and efficient.Another object is to provide a resistance medium or device havingcertain desired characteristics in operation and freefrom certainundesirable characteristics. Another object is to provide an electricalresistance medium which is of simple construction and inexpensive.Another object is to provide a device of the above nature which isdurable and capable of dependable service without ageing ordeteriorating. Other objects will be in part obvious or in part pointedout hereinafter.

The invention accordingly consists in the features of construction,combinations of elements, and arrangements of parts as will beexemplified in the structure to be hereinafter described, and the scopeof the application of which will be indicated in the following claims.

This case is a division of application filed May 28, 1925, Serial No.33,327, which issued as Patent 1,771,055; July 22, 1930.

In the accompanying drawings, in which is shown one of the variouspossible embodiments of my invention Figure 1 illustrates somewhatdiagrammatically the insulating fiber forming part of my resistancedevice, at a certain stage in the manufacture thereof, and

Figure 2 shows somewhat diagrammatically my resistance device at variousstages in its course of manufacture.

Similar reference characters refer to similar parts in both views of thedrawin s.

Referring now to the drawings in etail, there is shown in Figure 2 aroll 10 upon which is wound a continuous fiberlike or threadlike memberof non-conducting material shown passing from the roll 10 at 11. Thisnon-conducting fiber or thread is referably of glass, glass havincertain a vantageous characteristics which will be later pointed out,but it is to be understood that other non-conducting material might beemployed to advantage.

This glass fiber 11 is preferably formed as 1s\i llustrated in Figure 1.A glass rod 12, for e zample, about three-eighths of an inch indiameter, is fed. endwise through a heating medium, in this instanceshown as a gas flame 13. As the rod is fed through the heating medium'13 its end is softened, and this softened end is grasped, drawn out, andwound upon the roll 10, formin the fiber 11. The roll 10 is driven, inthe irection indicated by the arrow in Figure 1, at a rate of speedwhich is predetermined with respect to the rate of feed of the rod 12,into the heating medium 13. Preferably the roll or spinning wheel 10 andthe mechanism driving the rod 12 through the heating medium 13 are bothdriven from a common source of power, so that there is thus maintamed aconstant ratio between the speed at which the filament 11 is pulled outand the speed at which the rod is moved into the heating medium. In thismanner the lass fiber or thread 11 is drawn out in a uni orm d1ameter,providing the diameter of the glass rod 12 is uniform. Preferably theheating element 13, the speed of movement of the rod 12 and the speed ofrotation of the roll 10 are so proportioned that the glass fiber 11 isuniformly drawn out to a diameter in the neighborhood of two-hundredthsof an inch. The word fiber as used in the claims is to be construed tomean a filament of the order of one-twentieth of an inch or less.

Referring now again to Figure 2, the glass fiber 11 is rawn from theroll 10 and, after passing through various mechanisms which will bedescribed in detail herein, is gripped between a pair of driven rollers14 and 15. The peripheries of these feed rollers 14 and 15 arepreferably covered with a yielding material such as leather, and theserollers grip the glass fiber 11, drawing it from the roll 10 through thevarious mechanisms which will presently be described.

Referring now to the right-hand side of Figure 2, the lass fiber 11 asit is drawn from the roll 10 first passes over a curved andtrough-shaped guide 16. The guide 16 at its lower end pro erly positionsthe lass fiber for passage t rough a coating ,evice 17.

This device 17 is preferably in the form of a T-tube having a horizontalpassage 18 through which the fiber 11 is drawn and a vertical passage 19communicatin at its upper end with the first passage. container such asa bottle 20 contains the material, in the form of a fluid, with whichthe fiber 11 is to be coated in the coating device 17. The lower end ofthe bottle 20 is connected by a flexible tube 21 with the mouthof thevertical passage 19 in the coating device. The bottle 20 is preferablyadjustable in a vertical direction, as by means of an adjusting screw22.

As was mentioned above, the material with which the fiber 10 is coatedin the coating device 17 is contained in the form of a liquid or asolution in the bottle 20. This material, indicated at 23, com risespreferably minute particles of a suita le electrical conducting materialsuspended in a suitable solution. A satisfactory material is carbon inthe form of extremely minute (almost colloidal) particles suspended insolution. The character ii of the solutions employed will later bepointed out more fully herein. By adjusting the height of the bottle 20,the solution fills the tube 21 and rises through the passage 19, fillingthe passage 18 through which the glass fiber 11 is drawn. Capillaryaction prevents the solution from flowing out of the ends of thehorizontal passage 18. As the glass fiber is drawn through the passa e18 it is coated with a thin layer or film o the solution of conductingmaterial; the thickness of the film deposited uponthe fiber may becontrolled by adjustments of the height of the bottle 20.

The glass fiber thus emerges from the coating device 17 covered with athin moist coating of the conductin material contained in solution inthe bott e 20. The fiber now passes through a drying device 24 which isheated by suitable means illustratively shown as an electric light bulb25. In this drier 24 the moist conducting coating or film is dried.

The glass fiber now passes through a heating device or furnace 26wherein it is subjected to a more intense heat, wherein all moisture ispositively driven from the glass fiber and from the conducting coatingthereon, and wherein certain other chan es take lace, which will laterbe describe This urnace preferably takes the form of an elongated tubeas shown, heated for example, by means of a Bunsen burner 2 Air ispreferably excluded from the furnace 26 as the coated glass fiber passestherethrough, and it is found advantageous to substitute for the air anatmosphere of certain gases. For this purpose hydrogen is found to beparticularly advantageous. A supply of hydrogen is connected with theinterior of the heating tube adjacent its right-hand end as 28,

insane and the hydrogen is permitted to escape adually through theopening 29 at the leftand end, through which the glass fiber passes fromthe furnace. In order to prevent exit of hydrogen from the right-hand orentering end of the furnace, this end is sealed by suitable means suchas mercury 30 which prevents exit of the hydro on, but permits readydrawing of the glass ber 11 therethrough. The mercury is introducedthrough an upper opening 31 and cannot flow out through the restrictedpassages 32 and 33 on either side thereof through which the glass fiber11 is drawn. The atmosphere of hydrogen, among other advantages attainedthereby, prevents oxidation of the conducting coating.

From the furnace 26 the glass fiber is drawn through a second coatingdevice 34. In this coating device there is applied to the glass fiber,exteriorly of the conducting coating, a film of a suitable protectivematerial in the nature of a binder which is adapted to hold theconducting coating in place upon the glass her and prevent itsaccidental rubbing off. The device 34 preferably takes the form of aT-tube having a funnel-shaped upper mouth 35 through which theprotective solution 36 is introduced. I Capillary action prevents thesolution fromrunning out of the two horizontal openings through whichthe glass fiber is drawn. The material 36 preferably comprises asolution of rosin in benzol, and a thin film of this solution isdeposited exteriorly of the conducting coating as the glass fiber passesthrough the device 34.

Upon emerging from the coating device 34 the glass fiber passes througha heating de vice or drier 37 similar to the drier 24. In the drier 37the benzol is driven off and a thin layer or film of rosin remains overthe conducting coating. By adjusting the concentration of thebenzol-rosin solution, the thickness of the film given in the device 34may be controlled. In order that the resistance value of a length of theresistance device of the invention may be substantially that of thecarbonaceous coating, unaffected by the film of protective material, theprotective film should be of good insulating substance, rosin being sucha substance. Preferably the concentration of the benzol-rosin solutionis adjusted so that the protective film will be very thin; so thin thatit will not appreciably alter the value of resistance of a length of theresistance with the current passing through (not along) the film, intothe conducting coating, for the purpose of measuring the resistance ashereinafter described, or otherwise.

The glass fiber now preferably passes through a device 38 containing twomercury contacts 39 and 40 spread a predetermined distance apart. Acrossthese two contacts is connected a battery 41 and a suitable resistancemeasuring device 42, which may be an ordinary megger. The megger 42 thusgives a constant reading of the resistance of the conducting coating pergiven length of the glass fiber, and this resistance will remalnsubstantially constant and uniform.

The coated glass fiber now passes through between the feeding rollers 14and 15 which, as was mentioned above, draw the fiber through the seriesof devices just desorlbed. Emerging from the feed rollers 14 and 15, theglass fiber passes through a suitable gu de 43. Adjacent the left-handend of the guide 43 is a solenoid 44 fed by the battery 45 and providedwith a plunger 46. The lower feed roller 15 is provided on its peripherywlth a projecting contact 47 which, at each rotation of the roller,strikes a spring contact 48, complotting the circuit of the solenoid 44.Thus at each rotation of the roller 15 the plunger 46 is drawn upwardlyand breaks off the glass fiber emerging from the left-hand end of theguide 43. The coated glass fiber is thus cut into predetermined lengthsby the plunger 46 and these lengths are received in a suitable trough49. In Figure 2 one of these lengths 50 is shown after it has beendropped into trough 49.

Considering now more particularly the nature of the material employed informing the conducting coating upon the glass fiber, it has been pointedout above that a satisfactory material is carbon in the form of minuteparticles suspended in a solution. Excellent results are obtained byemploying either a suspension of carbon in an aqueous solution ofglue-like material or a suspension of carbon in a liquid hydrocarbon. Asan example of the latter, a solution of lamp black and 11nseed oil maybe employed. As an example of the first, a mixture of Le Pages glue andlampblack in substantially equal parts mixed into a paste and thendiluted with water to the desired consistency gives satisfactoryresults; Another solution which gives excellent results is thecommercial Higgins carbon drawing ink. This ink is a solution of carbonand appears to contain a glue-like constituent.

In the furnace 26, the temperature employed is preferably kept withinthe limits of 700 and 1350 F. The best results are obtained when atemperature in the neighborhood of 1200 or 1300 F. is employed. Aneffect of this baking in the furnace 26 is to drive off the volatileconstituents of the glue or other material mingled with the carbon,leaving practically a pure carbon film. The glue is carbonized by theheat and the particles of carbon resulting therefrom appear to fill theinterstices between the carbon particles which were suspended in thesolution, so that a solid uniform coating of-carbon results.

From the foregoing, it will be seen that my invention is one welladapted to attain the ends and objects hereinbefore set forth in apractical and efiicient manner, and that my resistance device is oneembodying practical advantages of great importance.

The glass fiber being non-porous and the conducting coating beingthoroughly dried and covered with a non-hygroscopic film, the resistancedevice is stable in its resistance, being unaffected by changes intemperature and not suscepible to variations in its moisture content,due to weather conditions or other conditions of use. The conductingcoating is deposited upon the glass fiber in such manner that it may beformed in an extremely thin film which is of a definite andsubstantially unvarying thickness throughout. These characteristics andothers render this resistance device of particular advantage when usedinwireless-receiving apparatus and other sound amplifiers. the devicebeing particularly well adapted for use in the so-called grid-leakcircuit of wire ess-receiving apparatus. It is found that thisresistance device is non-microphonic, that is, it produces no hiss orfrving noise when employed in a-sound amnlifving apparatus. advantagesare attendant upon the use of carbon as the conducting film. althoughthis invention in its broadest aspects is not limited to the us ofcarbon. In addition to the advanta es pointed out above, the temperaturecoefiicients of glass and carbon are approximately the same, andtherefore the glass-supporting fiber and the carbon film expandapproximately equally under heat. so' that there is no tendency tocrack. Experiment would seem also to indicate that certain of theseadvantages accrue directly from the use of a glass or similarnon-conducting fiber of very small diameter as a support for the,hip'hresistance conductive film of carbon. These results are of much greaterconsequence than might naturally be expected to follow a mere reductionin cross section. One of these results is noticeable in relation to thelongitudinal expansion of the mem- Particular ber under the heatingeffects occurrring in the use thereof, while another appears when thetransverse expansion thereof under like conditions is considered. Inuse, these coated filaments or fibers are mounted ri idly at their endsin a mass of some suitable metallic alloy, as, for instance, type-metal,which closes tightly about the carbon film and makes contact therewith.

In the case of a resistance element having a glass rod of reallyappreciable diameter as a support for the conductive material, thelongitudinal expansion of said rod, when heated, and its subsequentcontraction when cooled, often causes a. transverse fault to occur inthe conductive coating, adjacent the point where the glass enters theterminal members. Such cracks or faults inevitably cause hissing orfrying noises when such a device is used as a grid-leak in a radioreceiver. My device is substantially free from this great defect largelybecause of the pliability of the small glass fiber which permits theresistance ele- I ment to bend or warp slightlybetween its points ofcontact with the metal mounting. In this way, cracking of the conductivecoating is prevented, or if it occurs at all, it is to so slight adegree as to produce no noticeably audible disturbance.

Also, when a resistance element of relatively large diameter is heatedas mentioned above, it is subject to lateral or circumferentialexpansion within the metal alloy. Under these conditions the glasssupport may be crushed, the carbon film fractured or distorted, or themetal may be forced to recede from its close contact with the element.In any one of these cases the device becomes practically useless. If theglass is crushed it is ruined. In case the film is fractured ordistorted, microphonic faults occur, which render the grid-leakunsatisfactory in use, and should the third condition arise, namely, thewithdrawal of the metal from its close contact with the carbon film,then and thereafter imperfect contact results, which again produceshissing and frying noises when the device-is used as a grid-leak.

It should be noted further that grid-leaks of very small dimensions,both as to length and diameter, may be made with the present coatedfiber and yet have the high resistance values necessary in practicaluse. Resistances of circular cross section vary in absolute resistanceinverse-1y as the square of their diameters, and directly in proportionto their lengths. This is true whether the conductor be a tube or solid,providing when tubular conductors are compared the same thickness ofconductive material is maintained. Thus, in order to obtain ahighresistance of the order now under consideration with a resistancedevice having a relatively large rod as a support, the devices mustattain relatively great lengths, but resistances made in accordance withmy invention, with their fine fiber support and film of conductivematerial, may be produced in units of very high resistance withoutexceeding in length the standards established as desirable in radiodesign.

As many possible embodiments may be made of the above invention, and asmany changes might be made in the embodiment above set forth, it is tobe understood that all matter hereinbefore set forth or shown in theaccompanying drawings is to be interpreted as illustrative and not in alimiting sense.

I claim:

1. In an electrical resistance device, in combination, a glass fiber ofsufficiently small diameter to be pliable, and a coating of solid carbonof'substantially uniform thickness and continuity upon the surface ofsaid. fiber, said coating consisting of fine carbon particles and acarbonized material filling the interstices between said articles, saidcoating bein of a thickness and texture to be pliable, wit out ruturing, throughout the range of pliability 0? said glass fiber.

2. In an electrical resistance device, in combination, a glass fiber of;sufiiciently small diameter to-be pliable, and a coating of solidcarbonaceous material of substantially uniform thickness and continuityupon the surface of said fiber, said coating being of a thickness and atexture to be pliable, without rupturing, throughout the range ofpliability of said glass fiber.

3. In an electrical resistance device, in combination, a glass fiber ofsufiiciently small diameter to be pliable, a coating of solidcarbonaceous material of substantially uniform thickness and continuityupon the surface of said fiber, said coatin being of a thinness and atexture to be pliable, without rupturing, throughout the range ofpliabihty 0 said glass fiber, and a non-hygroscopic protectiveinsulating film upon said coating.

In testimony whereof, I have signed in name to this s ecification thistwenty-fourth day of June, D. 1929.

HAROLD FENDER.

